Combine avocado, garlic, scallion, jalapeno, cilantro, water, vegetable oil, lime juice, vinegar and honey in a blender and season with salt and pepper. Blend on high speed until smooth. Taste and adjust seasonings as needed.
Preheat a grill to medium-high.
Drizzle red and yellow bell peppers with olive oil. Season with salt and black pepper.
Discard dark green outer husks of corn, leaving inner husks intact. Peel back inner husks halfway and pull off the silk. Wrap cobs back in their husks.
Arrange bell peppers and corn on the grill. Cook, flipping peppers and turning corn occasionally, until peppers are lightly charred on both sides and corn kernels are bright yellow and lightly toasted, 8 to 10 minutes. Transfer vegetables to a cutting board. Coarsely chop peppers and cut corn kernels off cobs. Let cool.
Place vegetables in a large bowl, and add grains, lettuce and scallions. Toss with enough dressing to coat. Season with salt and black pepper to taste. Top with pepitas and cheese. Serve with remaining dressing on the side.