Line a half sheet rimmed baking tray with parchment. Set aside.

Add the lentils and bouillon to a medium saucepan, along with 480 milliters (2 cups) water.

Bring to a boil. Reduce heat to medium and cook, topping up with additional water as needed. Continue cooking until lentils turn mushy, about 40 minutes.

Scoop cooked lentils into a bowl and set aside to cool, about 20 minutes.

Meanwhile, preheat oven to 400° F / 205° C.

Heat the olive oil in a large saucepan. Add the carrots, celery, and garlic and cook until vegetables soften, about 5 minutes.

Stir in the tomato paste and cook 30 seconds more. Remove from heat.

Transfer vegetables to a small bowl. Set aside to cool slightly, about 5 minutes.

With a fork, mash the lentils until a thick, chunky paste forms. Some pieces of lentil should remain visible.

Add the dried oregano, dried basil, dried thyme, garlic powder, kosher salt, ground black pepper, and egg, and stir until well combined.

Stir in the vegetable mixture.

Stir in the rolled oats.

Stir in the chopped parsley.

With clean hands, roll the mixture into golf ball-sized meatballs. You should have about 24-26 total.

Arrange on prepared tray.

Spritz tops of meatballs generously with olive oil spray.

Bake in preheated oven for 15 minutes, or until tops of the meatballs look slightly dry and golden brown. Toss with a metal spatula, or use your hands to turn each meatball. Spritz with additional oil. Cook 10 minutes more.

Serve hot.

Store leftover meatballs in an airtight container in the refrigerator for up to three days, or freeze in an airtight container for up to 3 months.