1. Heat oven to 400°F. Stack tortillas on a large square of foil and wrap them loosely.
2. In a large skillet, heat oil over medium-high heat. Add onion and garlic; sprinkle with 1 tsp. salt and 1/2 tsp. pepper. Cook, stirring occasionally, until vegetables soften, 3 to 5 minutes.
3. Crumble tofu into skillet with your hands. Cook, stirring and scraping bottom of skillet occasionally and adjusting heat as necessary, until tofu browns and crisps as much as you like, 10 to 30 minutes. When tofu is almost ready, put tortillas in oven.
4. Add bell pepper to skillet, if desired. Sprinkle mixture with chili powder; stir and cook, scraping any browned bits from bottom of skillet, until mixture is fragrant, less than 1 minute. Squeeze halved lime over mixture and garnish with cilantro and scallions. Serve with tortillas and lime quarters.