Preheat broiler to high. Lay bell pepper and Fresno chile peppers on a baking sheet and broil until the skin of the peppers is blackened, about 10-12 minutes. Rotate the peppers while broiling to allow all sides of the pepper to blacken. Remove from heat and transfer to a bowl. Cover with plastic wrap and let steam for 10 minutes. Remove cover and carefully peel and discard skin and seeds.
Toast caraway seeds, coriander, and cumin in a skillet over medium heat until fragrant, about 2 minutes. Remove from heat. Combine seeds, roasted peppers, garlic, juice of lemon, olive oil, and salt and pepper in a blender or food processor. Puree until smooth. Whisk together 1 - 3 tablespoons of harissa with mayonnaise, adding more harissa for a spicier condiment. Reserve remaining harissa for another time.
Combine ingredients for hummus including black beans, the juice from the canned beans, tahini, lemon juice, and garlic in a blender or food processor, and puree until smooth. Season with salt and pepper.
Toast sliced bread. Spread black bean hummus on each slice. Top with sliced avocado, chopped tomatoes, and chopped green onions. Drizzle harissa aioli and sprinkle sea salt. Serve.
Notes
The harissa aioli and black bean hummus can be prepared up to 3 days in advance.