Add eggs to lentils in a mixing bowl. Stir well to combine, then start adding cornmeal. You're looking for the texture to be something like soft drop biscuits. It's a bit wet and sticky, but it'll hold shape for a moment when squished up with the spoon. If it's too wet, add more cornmeal. If it's too dry, add another egg, more cooked lentils or a tiny bit of water.
Add seasonings as you prefer. I like to give mine a couple of good shakes of garlic powder, pepper and salt, a few pinches of rosemary, some thyme and maybe 1/2 tsp sage. Sometimes I add finely minced onion, onion powder or parsley. They're also really good with Italian seasoning, curry powder, chilli powder and turmeric, or taco seasoning. Try a sausage seasoning blend such as This One if you're going for a more sausage flavour. Don't be too shy with the spices. The natural starchy mild sweetness of lentils and cornmeal can handle quite a bit of added flavour.
Heat oil in a heavy frying pan. I use a small cast iron pan for these. It doesn't take a ton of oil, gets great heat distribution and retention, and it's easy to clean up. Add around 1/2 inch oil to the pan and put it over medium to medium-high heat until the oil sizzles when you toss a bit of batter in.
Scoop portions of batter into the oil and flatten slightly into a puck with the back of the spoon. You can use a spoon for this, but it tends to stick to the spoon. I find it's much faster and easier to use a scoop similar to an ice cream scoop. It makes nice, reasonably uniform size and shape patties that cook about the same rate and add to the burger patty look.
Cook until you see browned edges on the bottom, then flip and brown the other side. Depending on the moisture level and how hot your oil is, it takes a couple of minutes per side. I've never measured the oil temperature; I prefer to keep an eye on the patties and judge by when they're browned and crisp on the outside.
Remove from pan with a slotted spatula, letting excess oil drip back in the pan. Move to a plate lined in several layers of paper towel to drain.
Repeat scooping, brown, flip, brown and drain with all remaining batter.