Put quinoa, lentils, water, garlic and 1 cup water in a pot. Bring to a boil, then cover and lower heat to a simmer. Cook until lentils and quinoa are tender and water has evaporated, about 20 minutes. Set aside to cool.
Put onions, carrots and jalapeño peppers (if using) in a food processor. Pulse until very finely chopped.
Transfer cooked garlic from lentils to a large bowl and mash it. Add black beans and mash with a potato masher until you have a rustic consistency. Add cooked lentils and quinoa, chopped vegetables from the food processor, flour, Mexican seasoning, oregano and salt.
Mix everything together using your hands. Scoop mixture into 10 balls and flatten them into patties. Cook in a lightly oiled skillet over medium-high until lightly browned, 3 to 4 minutes on each side. Or bake in a preheated 375°Foven until lightly browned, 4 to 5 minutes each side.
Serve sliders on buns with condiments and toppings of your choice