Preheat the oven to 400 F
Add the walnuts, lentils, carrots and diced onion to a food processor or blender. Pulse the mixture for 20-30 seconds. Scrape down the sides and pulse again for another 20-30 seconds. The mixture should be mostly mashed, with some thicker pieces still remaining- not a complete paste.
Transfer the mixture to a bowl and add in the spices, balsamic, lemon zest and flour. Combine everything together using your hands.
To make the burgers, I like to wet my hands or add some oil between my hands so the mixture is easier to work with. Take about ¼ cup of the mixture and shape into mini patties.
Place the burgers onto a parchment lined sheet pan. Drizzle them lightly with olive oil
Bake them for 20-25 minutes total, flipping them halfway through. I like to add another light drizzle of olive oil when I flip them. Alternatively, you can grill them in a pan with a little olive oil on medium heat for about 2-3 minutes per side.
The baked burgers can be refrigerated for up to 5 days, or frozen for up to 3 months.