1. Bring a pot of water to a boil. Set asparagus tops aside and add asparagus stems to boiling water. Cook until just tender, 2 min. Scoop out and rinse under cold water. Pat dry, then whirl with spinach, shallot, parmesan, pine nuts and salt in a food processor. With motor running, add 3 tbsp oil through feed tube until smooth, 1min.

2. Cook pasta in boiling water following package directions but omitting salt, until tender, 9 min. Reserve cup pasta water, then drain.

3. Heat a large non-stick frying pan over medium-high. Add remaining 1 tbsp oil, then shrimp and asparagus tops. Cook until shrimp turns pink, 2 to 3 min. Add garlic and cook until fragrant, 1 min. Stir in pasta, pasta water, spinach pesto and lemon zest. Divide among four plates, then serve with lemon wedges.