Process ⅓ cup coarsely chopped onion, ⅓ cup coarsely chopped carrot and ⅓ cup coarsely chopped celery until they are mixed but don't start to turn into a paste.
Add 1 cup cooked rice, ½ teaspoon salt, ⅛ teaspoon freshly ground black pepper, ⅛ teaspoon smoked paprika, and 2 tablespoons chopped parsley. Process until it's all mixed, but with texture; don't turn it into a paste.
Add 2 eggs and process until combined. It will be soupy or at least very thin.
Add ¼ cup oats. Process using on/off just to mix a bit. It has to come together, but not be completely integrated.
Only now add 1 cup cooked lentils (see Notes below) and ½ garlic clove if using, and process until you have a thick mixture and can it mounds well on a spoon. Don't process the lentils. The whole mixture should be integrated, but not a paste or very smooth. It has texture.
Sprinkle oatmeal on a plate. Form the hamburgers by scooping a portion, forming it into a ball, and flattening it into a patty.
Place on top of the oats, add some extra oats to the top of the patties and press slightly to adhere on both sides.
Store in the refrigerator for up to 2 days, well wrapped or in a container with a lid. Or freeze up to a month, individually wrapping each one and putting them in a container so they keep their shape while freezing.
Preheat the oven to 350°F (180°C).
Put the burgers on an oiled baking sheet, and drizzle with some oil. I use olive oil, but any type will do.
Cook for 10-15 minutes and turn, cooking an extra 5-10 minutes until done.
Pizza-style burgers: When you turn them over, top the cooked side with tomato sauce and melty cheese (as you would a pizza). Continue baking until the burger is done (egg cooked) and the cheese is melted.