Heat oven to 425°F and put a large pot of heavily-salted water on to boil for the pasta.
Heat olive oil in a large frying pan over medium-high heat. Once shimmering, add onions and red bell peppers. Cook, stirring occasionally, until beginning to soften, about 8 minutes.
Add zucchini, kale, garlic, ancho chile, and salt, and continue cooking 5 more minutes.
Add tomatoes, oregano, and water and bring to a boil. Taste and add more salt as needed. Remove from heat while you cook the pasta.
Once the pasta water is boiling add rigatoni and cook for only 5 minutes. Drain and return to the pot. Add tomato sauce and toss to coat. Transfer to a 9 x 13in baking dish.
Dot with requesón, cover with mozzarella and bake until golden brown and bubbly, about 30 minutes. Remove, sprinkle with Cotija and serve.