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.
The Sauce:
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.
Assembling:
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.