In a small pan, heat the olive oil over medium heat. Add the red onion, zucchini, red and yellow capsicums, and mushrooms. Sprinkle it with chili powder, salt, and pepper. Sauté until the vegetables are tender and slightly caramelised, about 3-4 minutes. Remove from heat and set aside.
Spread the toasted English muffin halves with a layer of refried beans. Sprinkle the shredded cheese on top of the beans.
Place the prepared muffin halves under the grill until the cheese is melted and bubbly, about 2-3 minutes. Keep a close eye to prevent burning.
To assemble the muffin first top the melted cheese with sautéed vegetables, distributing them evenly over each muffin. Dollop with sour cream, then add avocado slices on top. If desired, add sliced jalapeños on top of the avocado. Finish and with chopped fresh coriander and a squeeze of lime.
