Step 1

Place beans, quinoa, panko, scallions, tomato paste, cumin, chile powder, garlic powder, 1/4 cup mayonnaise and 1/4 teaspoon salt in a large bowl; mash the mixture together with your hands. Shape into six 3/4-inch-thick patties. Arrange the patties on a plate; refrigerate for 10 minutes.

Step 2

Combine avocado, lime juice, cilantro, water and the remaining 1/4 cup mayonnaise and 1/4 teaspoon salt in a food processor; process until smooth, about 30 seconds.

Step 3

Heat oil in a large cast-iron skillet over medium-high heat. Add the patties; cook until golden brown, 3 to 4 minutes per side.

Step 4

Divide the avocado mixture evenly among top and bottom bun halves. Arrange the bean patties and tomato slices evenly on the bottom bun halves; replace the top bun halves.