Cook the lentils: In a medium saucepan, combine 1 cup of brown lentils with 3 cups of water. Bring the mixture to a boil, then reduce the heat to low and let simmer for 25-30 minutes or until tender. Drain excess water and set aside.

Sauté the vegetables: In a large skillet, heat 2 tablespoons of olive oil. Add 1 chopped onion, 2 minced garlic cloves, 1 diced carrot, and 1 diced celery stalk. Sauté for 5-7 minutes until softened.

Mix the ingredients: In a large mixing bowl, mash the cooked lentils. Add the sautéed vegetables, 1 cup of rolled oats, ½ cup of breadcrumbs, 1 flax egg, 2 tablespoons of soy sauce, 2 tablespoons of tomato paste, 1 teaspoon of dried thyme, 1 teaspoon of smoked paprika, and season with salt and pepper. Stir until well combined.

Prepare the glaze: In a small bowl, whisk together ½ cup of ketchup, 2 tablespoons of maple syrup, and 1 tablespoon of balsamic vinegar until smooth.

Shape and fill: Preheat oven to 375°F. Line a loaf pan with parchment paper. Transfer the lentil mixture into the loaf pan, pressing down firmly. Spread the glaze evenly over the top.

Bake the lentil meatloaf: Place in the oven and bake for 45-50 minutes until golden brown and edges are crispy. Let cool for 10-15 minutes before slicing.

Serve and enjoy: Slice into thick portions and serve with creamy mashed potatoes or a fresh salad.