Heat 1 teaspoon olive oil in a medium skillet set over medium heat. Add onion and sauté until soft. Add garlic, chipotle pepper, cumin, salt and pepper. Saute for additional 2 minutes.

Scrape the mixture into the food processor. Add black beans, brown rice and lime juice. Pulse until the beans are chopped, but not pureed.

Scrape the black bean mixture into a large bowl. Add the breadcrumbs and the cilantro. Stir the mixture until combined.

Divide the mixture into 8 equal portions (about ¼ cup each) and form into patties. If the mixture is too moist to form patties, add more breadcrumbs.

Place the patties on a baking sheet lined with plastic wrap and cover with additional plastic wrap. Refrigerate for at least 30 minutes.

Heat 1 tablespoon canola oil in a large skillet (preferably not nonstick, so a good crust can form) set over medium heat. Add the patties and cook for 3 minutes per side. If the skillet is not large enough to fit all of the patties, cook them in two batches.

While the patties are resting in the fridge, make the sauce.

In the bowl of a food processor, combine the avocado, cilantro, yogurt, lime juice, olive oil, chipotle pepper and salt. Puree until smooth.

Divide the avocado sauce between the rolls (about 1 tablespoon plus 1 teaspoon sauce per roll). Top each with one black bean patty and one slice of tomato. Serve.