1. Simmer beans and their liquid in a small saucepan until warm. Purée in a food processor or blender. Set aside.
2. In a small bowl, whisk together 2 tbsp. oil, the lemon juice, garlic, parsley, and 1/2 tsp. salt, and set aside.
3. Heat remaining 1 tbsp. oil in a large frying pan over high heat. Add scallops and cook, turning once, until starting to brown and slightly firm to the touch, about 2 minutes. Add butter and stir scallops to coat in butter. Remove from pan and sprinkle with 1/2 tsp. salt. Add asparagus to same pan and cook, covered, until tender-crisp, about 6 minutes.
4. Divide bean mixture among 4 plates. Top with scallops and asparagus and drizzle with dressing.
Make ahead: Combine dressing components up to 2 hours ahead.
Note: Nutritional analysis is per serving.