Preheat the oven to 375°F.
Add the walnuts to a food processor and pulse a few times until roughly chopped.
Add the onion, garlic, and bell pepper, and pulse until finely chopped.
Heat olive oil in a large skillet over medium heat. Add the walnut-vegetable mixture and cook 4-5 minutes, until the vegetables are softened.
Stir in the canned lentils and spices, mixing until well combined.
Lay the tortillas flat on a baking sheet. Spoon the walnut-lentil mixture onto half of each tortilla and top with cheese.
Bake 3-4 minutes, until the cheese melts. Remove from the oven, fold the tortillas in half, and lightly spray both sides with cooking spray.
Return the folded tortillas to the oven and bake 15–20 minutes, flipping once halfway through, until golden and crispy.