Preheat the oven to 375°F and lightly oil a baking sheet. Spread out the tortilla strips, season with chili powder, salt, and pepper, toss to combine, then arrange in a single layer. Bake until crisp and golden, about 10–12 minutes, tossing halfway through. Set aside.
Heat the olive oil in a large stockpot over medium heat. Cook the onions, green pepper, and jalapeño until tender, 5–7 minutes.
Add the garlic, tomato paste, chili powder, and cumin, and continue to cook until the garlic and spices are fragrant, about 2 minutes.
Stir in the vegetable broth, crushed tomatoes, water, cilantro, and a quarter of the baked tortilla strips. Reduce to a simmer and cook uncovered for 30 minutes.
Stir in the quinoa, black beans, and corn. Simmer uncovered, until the quinoa is cooked, about 15–20 minutes.
Serve the soup with the remaining baked tortilla strips and your favorite toppings.