Not to worry—this huge amount of greens really does cook down. If you have access to fava flowers, they're a pretty garnish.
Heat a 12-in. frying pan over medium-high heat. Stir-fry one-third of fava leaves at a time with 2 tsp. oil and a pinch each of salt and pepper until greens wilt, 2 minutes. Transfer to a bowl; tent with foil.
Reduce heat under frying pan to medium-low. Add 3 tbsp. oil and stir in 1/2 tsp. each salt and pepper, the green garlic, fennel seeds, and lemon zest. Cook, stirring often, until garlic is softened, 5 minutes. Add wine and boil over high heat until reduced by half, 2 to 3 minutes. Reduce heat to medium. Add shrimp in a single layer and cook, turning once, until cooked through, 2 to 3 minutes.
Cook linguine as package directs. Drain, saving 1 cup water. Return pasta to pot and toss with shrimp mixture and remaining 1 tbsp. oil. Add fava leaves and toss, pulling apart with forks. Mix in pasta water if linguine seems dry, plus more salt and pepper if you like. Spoon into a serving bowl and top with fava flowers if you like.
*Find fava greens (and sometimes their flowers) and green garlic at farmers' markets. If you can't find green garlic, use 2 tbsp. minced regular garlic plus 6 tbsp. green onions.
Note: Nutritional analysis is per serving.