Place sweet baby broccoli and lemon slices on a rimmed baking sheet. Drizzle with olive oil and season with salt and pepper. Roast until tender and slightly browned, about 15-20 minutes.
Remove from oven and place on a platter or in a shallow serving dish.
While sweet baby broccoli is roasting, mix together broccoli leaves, pecans, garlic, lemon zest, parsley, Parmesan, salt and pepper. Drizzle lemon juice and melted butter over mixture and mix well.
Sprinkle gremolata over sweet baby broccoli and lemon slices, and serve!