How to Make It
Preheat oven to low broil with oven rack 6 inches from heat. Place pepper halves, skin side up, on a rimmed baking sheet. Broil in preheated oven 10 minutes. Remove baking sheet from oven. Scatter scallions and garlic cloves around peppers, and return to oven. Broil until peppers are blackened in spots and soft when pressed, about 10 minutes. Transfer peppers to a bowl, cover with plastic wrap, and cool 10 minutes.
Meanwhile, coarsely chop scallions, and place in a blender. Remove and discard garlic skins. Add garlic, yogurt, black pepper, 1 1/2 tablespoons of the lime juice, and 1/2 teaspoon of the salt to blender. Process until smooth, about 40 seconds, stopping to scrape down sides as needed.
Stir together cabbage, shredded carrots, honey, and remaining 1/4 cup lime juice and 3/8 teaspoon salt. Let stand until ready to use, tossing occasionally. Drain excess liquid before using.
Peel peppers; cut peppers into thick strips. Discard any liquid.
Arrange squash in an even layer on a rimmed baking sheet lightly coated with cooking spray. Broil until tender, 10 to 12 minutes. Chill until cool, about 15 minutes.
Spread about 1 heaping tablespoon of the yogurt mixture on each bread slice, and top evenly with pepper strips, squash, cucumbers, bean sprouts, avocado, cabbage mixture, and arugula. Cover with remaining 4 bread slices.