Preheat oven to 425˚. Toss broccoli with onions, garlic, and olive oil and spread out in a single layer on a sheet tray covered with parchment. Roast broccoli until starting to char, 15 to 20 minutes. Transfer to a food processor and pulse into small pieces (no bigger than a lentil). Measure out about 1 cup.
While broccoli is roasting, combine lentils and water in a medium pot. Bring to a boil, reduce to a simmer, and cook until lentils are tender, 23 to 25 minutes. If lentils are not tender and water has been absorbed, add more water and continue to cook. Drain off any excess water.
In a food processor, combine the cooked lentils, broccoli mixture, nuts, panko, herbs, salt, and pepper. Pulse a few times to start combining the mixture. Crack the egg in and pulse a few more times until the mixture is combined but the lentils are still holding shape. Set aside and let rest while the oven preheats to 425˚.
Take the lentil mixture and roll into 12 balls, roughly the size of a golfball. Place on a baking tray covered with parchment paper and brush with olive oil. Bake meatballs until browning and crisp, 25 to 30 minutes.
While the lentil bites are cooking, make sauce. Heat olive oil over medium-low heat. Add garlic and cook for one minute. Measure in heavy cream and the 1 teaspoon of lemon zest. Bring the sauce to a boil and let cook until it thickens slightly, 6 to 8 minutes. Stir in lemon juice at the end.
Divide the lentil bites into two bowls and drizzle sauce on top.
Notes
+ Lemon Cream Sauce lightly adapted from Martha Stewart.