Place the tomatoes, peppers, onion, garlic, walnuts, lentils, and seasoning in the inner pot of your electric pressure cooker. Stir in 6 cups (1410 ml) of the vegetable stock.
Close and lock the lid, making sure the steam release knob is in the sealing position. Cook on high pressure for 30 minutes.
When the cooking time is complete, do a quick release by opening the release knob and venting all the steam. When the float pin drops, unlock the lid and open it carefully.
Stir in the pumpkin puree, black beans, and 1/2 cup (120 ml) of remaining stock. Lock the lid back in place and allow the beans to warm through, about 5 minutes. If the chili is too thick, add the remaining 1/2 cup (120 ml) stock and stir well.
Serve with avocado, lime wedges, cilantro, and corn bread as desired.