Combine the dressing ingredients in a jar with a lid or a glass measure. Shake the jar or whisk if making in a measure cup.
Make the marinade for the shrimp. Add 2 teaspoons of the dressing to a bowl and refrigerate the rest of the dressing until ready to serve. Add the remainder of the marinade ingredients to the bowl. Stir together. Cover and refrigerate until 35-40 minutes before serving time.
Roast the whole bell pepper and pasilla pepper, if using, over a gas stove burner, turning every minute until charred black. You could also do this step on a broiler pan or tray (on foil for easy clean up), for 1-2 minutes on each side, under the broiler of the oven. Set aside to cool.
Once the peppers are cool, peel the charred skin off and discard. Remove the stem and seeds and slice each pepper into ¼" strips.
Prepare the salad. Add the lettuce to a bowl or divide between 3-4 single serving bowls. Make piles of each, avocado slices, mango, corn kernels, red pepper slices, Pasilla pepper slices, cucumber, tomatoes, red onion, and cheese on top of the lettuces in each bowl or in the larger serving bowl. Cover and refrigerate until ready to serve.
Just 35-40 minutes before you want to serve, add the shrimp to the marinade. Stir to coat. Set aside for 30 minutes.
Heat a cast iron or skillet over high heat with 1-1½ tbsp vegetable or avocado oil. Remove the shimp from the marinade and add the the hot skillet. Cook for 1½-2 mintues per side. Remove from the heat.
Cool for a minute before adding to the top of the salad or divide evenly between single serving salads. Pass the dressing with the salad or drizzle on the top.