In a blender, combine (drained) roasted red pepper (look for some without any added sugar), milk, avocado, lemon juice, garlic, crushed red pepper, and 1/4 tsp. salt (optional). Puree until smooth.
Heat roasted red pepper sauce in a skillet over medium heat, stirring occasionally, until heated through, about 3 to 5 minutes. Add zucchini noodles (ends removed, cut into spaghetti-like strands with a spiralizer, mandolin, or julienne peeler), stir to incorporate, and continue cooking until cooked to your liking, another 3 to 5 minutes.
Meanwhile, melt butter in large skillet over medium-high heat. Season scallops with remaining salt (optional). Cook scallops until golden brown on each side and translucent in the center, about 1 to 2 minutes per side.