Preheat the oven to 400 degrees Fahrenheit. Slice the ends off the zucchini and discard. Slice the zucchini into 1/4 inch thick discs. Slice the bell peppers into 1 inch strips. Select a medium-sized ovenproof dish. Arrange the sliced zucchini in the oven dish creating alternate rows, overlapping the vegetables as you go. You should be able to create alternating rows of zucchini and pepper strips until the dish is full.
Drizzle the olive oil over the arranged vegetables. Add the passata to a mixing bowl along with the oregano, garlic powder, chili powder, ground cumin, paprika, salt and pepper. Stir everything together well to combine. Please feel free to adjust the spices and seasoning to personal taste as desired. Be sure to adjust your macros to account for any changes.
Spoon the spicy tomato sauce evenly over the prepared vegetables. Ensure the vegetables are coated equally in the dressing. Transfer the dish to the oven to bake for 20 minutes or until the vegetables are just tender.
Remove the dish from the oven. Scatter the grated cheddar cheese evenly over the surface of the gratin. Return the dish to the oven. Bake for a further 8-10 minutes, or until the vegetables are softened and the cheese is golden and bubbling on top.
Roughly chop the fresh cilantro and scallions. Arrange sliced jalapeños over the surface of the gratin. Scatter over the chopped scallions and cilantro. Serve hot, accompanied by your favorite Keto Mexican main dish.