Remove stems and seeds from peppers. Thinly slice peppers lengthwise about 1/4 inch thick.
Heat oil in a large nonstick skillet over medium-high heat. Cook peppers for 3 minutes. Add scallions and 1/4 teaspoon salt, and cook until peppers and scallions are tender, about 4 minutes. Reduce heat to low. Add beans, and cook until warmed through, about 2 minutes. Add reserved canning liquid from beans, the pineapple, and 2 tablespoons hot sauce. Remove from heat. Let stand, covered, to keep warm.
Using tongs, hold tortillas over a gas flame until lightly toasted, about 30 seconds per side; transfer to a plate, and cover with a kitchen towel to keep warm.
Fill tortillas with bean mixture. Top with yogurt, cilantro, and remaining 2 tablespoons hot sauce (optional).
Pepper-scallion mixture can be refrigerated overnight. Reheat mixture with beans and pineapple.