In a small bowl, whisk together all of the ingredients for the chipotle vinaigrette. Set aside while you prepare the salad.
Heat a tablespoon of olive oil in a large skillet. When hot, add the corn kernels, diced zucchini and a pinch of salt. Sauté for 8 minutes until tender and lightly browned. Transfer to a bowl and let cool to room temperature.
In the same pan, heat 1½ tablespoons of olive oil. When hot, add the bell peppers, onions, and a generous pinch of salt. Sauté for 10 minutes until the vegetables have softened and lightly browned.
Stir in the cumin and chili powder and cook for 1 minute. Stir in the lime juice an cook for another 30 seconds. Remove from the heat and set aside.
Place the chopped romaine, scallions and cilantro in a large bowl or serving dish. Add the corn, zucchini, and black beans to the greens. Drizzle with the chipotle vinaigrette and gently toss to coat. Add the bell pepper mixture, and top with the diced avocado and queso fresco. Serve immediately.