Pick over lentils and remove and debris you find. Rinse in a fine mesh strainer and place in a medium saucepan. Cover with cold water by 2-3 inches and add 1 teaspoon salt. Bring to a boil over medium high heat. Reduce to a simmer and continue to cook until lentils are tender but still hold their shape, about 15-20 minutes. Drain lentils and place in a serving bowl.
Add minced garlic and one tablespoon of olive oil to the warm lentils. Set aside to cool slightly.
Meanwhile, make the onions. Heat olive oil over medium high heat in a large nonstick or cast iron skillet. Add onions and cook, stirring frequently, until they are beginning to brown, about 5-7 minutes. Reduce heat to medium low and continue to cook until onions are caramelized and dark golden brown, about 25 additional minutes. If the bottom of the pan is getting dark, add a tablespoon or two of water as you are cooking the onions to loosen any brown bits on the bottom of the pan if necessary.
Heat the grill. Divide and shape the ground beef into 4 patties that are about an inch thick and have a slight divot in the center. This will prevent the patties from ballooning up in the middle as they cook. Season the burgers generously with salt and pepper.
Once the grill is heated, clean and oil the grates. Grill burgers over medium-high heat until they are done to your liking (about 4 minutes per side for medium-well).
Cover burgers and let rest. While burgers are resting, finish the salad. Add lemon juice, remaining tablespoon of olive oil, chopped herbs and cherry tomatoes to lentils and stir to combine. Season to taste with salt, pepper and additional lemon juice if necessary. Add an additional drizzle of olive oil if the salad seems dry.
Serve burgers topped with caramelized onions and alongside the lentil salad and Pickled Beet Salad.