With the rack in the middle position, preheat the oven to 450°F (230°C). Line a baking sheet with parchment paper.
On the prepared sheet, toss the bell and cherry peppers with 1 tbsp (15 ml) of the oil. Roast, skin side up, for 25 minutes or until the peppers begin to brown. Place them in an airtight container, seal and let cool. Remove the skin and seeds.
In a blender, purée the peppers with the remaining ingredients until smooth. Season with salt and pepper. Set aside.
On the same baking sheet, toss the asparagus and green onions with the oil. Season with salt and pepper. Roast for 15 minutes or until the vegetables are tender, turning them halfway through cooking.
Spread half of the sauce on a serving platter. Top with the asparagus and green onions. Serve with the remaining sauce.