There are lots of options depending on your preference and any dietary restrictions.

The answer to the question, "how do I get lots of protein with little effort?" is actually the same as for omnis: protein powder, just made from plants. It doesn't taste good (no protein powder tastes good, pure protein tastes like bleh), but you can dress it up with other stuff to make a shake just like you would with dairy-based protein powder. My favorite combo is to use a plant milk, maple syrup, peanut butter, and then protein powder. The amount of syrup dictates how healthy (and tasty) it is. You can get powders made from different plants if you have allergies. I think my current one is based on rice.

Next up on the list of easy lazy protein is vegan transitional junk food. You can get fake meat stuff and cook it up quickly for a lazy protein-rich meal that also might help you out if you feel like having a comfort food but still want to eat like a vegan. Like fake nuggets or a fake burger. Because it's nearly always a frozen item, you can wait to buy it when it's on super sale at a bulk or overstock grocery store. I don't eat this stuff very often but I have seen it at a massive discount at shops lately. Keep in mind that some of it is arguably not vegan because it'se development (R&D) often uses animals.

Next up is semi-processed protein-rich foods: tofu, seitan, tempeh. Tofu is amazing if you learn how to cook it right (it's not a meat substitute don't cook it like meat it's its own yummy food cook it like people do in East Asia). Seitan is pretty common and is often the basis of the less-convincing (and therefore imo better) meat substitutes. Tempeh is also yummy and imo tastes best in Indonesian food. IMO tofu is the best bang for your buck on protein + nutrition, on average. $2 for a pack that has 30 g of protein.

Finally, whole foods. Pulses and grains will be the leaders of this category. Anything bean-like or any high-protein grain. Even pasta can have a decent amount of protein in it (durum flour). Lentils are a classic poverty food and have incredible nutritional value to cost ratio. I recommend eating lentils regardless, they are very nutritious. Other good options are chickpeas, red beans, black beans, whole urad dal, toor dal. Buying canned beans is fine but you'll really get into money-saving territory if you buy dry beans and cook them yourself.

Preparing dry pulses can be done with two methods. The first method is the traditional way, where you soak them in water for at least 8 hours, usually overnight, and then cook for 30-60 minutes (red beans and similar need the most cooking m, otherwise they're a little poisonous). This method also produces a better texture and flavor. The second method is to use a pressure cooker, just cooking for 15-45 minutes depending on the pulse variety. This method is the most convenient because you don't have to plan your meal the day before or in the morning. Instant pots are great if they're in your budget (they are often on sale for about $60). A simple pressure cooker that has a whistle will cost $15-$20.

There are tons of really good and fairly simple foods you can make from everything I've listed. Let me know if you'd like some dish recommendations!