Heat oil (2 Tblsp) in a large pot over medium heat until shimmering.
Once hot, sauté poblano pepper (1), yellow onion (1), jalapeno (1), green bell pepper (1), and garlic (4) for 10-15 minutes, until onions are slightly translucent.
Add sweet potatoes (~6 c), mushrooms (8oz), walnuts (1c), seasonings (4Tblsp chili powder, 2tsp red pepper flakes, 2tsp cumin, 1tsp salt, 1 tsp garlic powder, 1 tsp paprika), and flour (1/4c). Sauté for another 5 minutes.
Add liquid (3c), tomatoes (28oz), and red lentils (1/2c).
Bring to a boil over medium-high heat, then reduce to medium-low heat and simmer for 30-40 minutes, until lentils are cooked and sweet potatoes are fork-tender.
Add black beans (1 can) and kidney beans (1 can) and cook for additional 3-5 minutes, until beans are warm.
Taste and adjust seasonings as needed.
Serve warm with avocado, brown rice, cilantro, and/or chips.
Keeps in refrigerator for 4-5 days in a sealed container. Keeps in freezer for ~1 month in a freezer-friendly container.