Step 1

Adjust oven rack to middle position and heat oven to 450 degrees. Heat 1 tablespoon oil in large saucepan over medium heat until shimmering. Add half of onions and ½ teaspoon salt and cook until softened, about 5 minutes. Stir in chili powder, cumin, sugar, and half of garlic and cook until fragrant, about 30 seconds. Stir in tomato sauce and water, bring to simmer, and cook until slightly thickened, about 7 minutes. Season with salt and pepper to taste; set aside.

Step 2

Meanwhile, heat 1 tablespoon oil in Dutch oven over medium heat until shimmering. Add remaining onions and ¼ teaspoon salt and cook until softened and just beginning to brown, 5 to 7 minutes. Add remaining garlic and cook until fragrant, about 30 seconds. Add chard and bell peppers, cover, and cook until chard is tender, 6 to 8 minutes. Using potato masher, coarsely mash half of beans in large bowl. Stir in chard-pepper mixture, ¼ cup sauce, and remaining whole beans.

Step 3

Spread ½ cup sauce over bottom of 13 by 9-inch baking dish. Brush both sides of tortillas with remaining 2 tablespoons oil. Stack tortillas, wrap in damp dish towel, and place on plate; microwave until warm and pliable, about 1 minute. Working with 1 warm tortilla at a time, spread ¼ cup chard filling across center. Roll tortilla tightly around filling and place seam side down in baking dish; arrange enchiladas in 2 columns across width of dish. Cover completely with remaining sauce.

Step 4

Cover dish tightly with aluminum foil and bake until enchiladas are heated through, 15 to 20 minutes. Let enchiladas cool for 10 minutes. Drizzle with cilantro sauce and sprinkle with avocado and cilantro. Serve with lime wedges.