Cook lentils: Rinse the lentils and add to a medium saucepan with the vegetable broth. Bring to a boil before reducing the heat. Simmer covered for about 30 minutes, or until just tender. Do not drain.
Make flax egg: Mix the flaxseed meal with ⅓ cup water in a medium bowl. Place in the refrigerator for at least 10 minutes.
Preheat the oven to 350ºF.
Cook aromatics: Heat a drizzle of olive oil or vegetable broth in a large skillet over medium-high heat. Cook the onion, carrot, celery, and garlic for about 5 minutes, or until the onion is translucent. Add the tomato paste, thyme, garlic powder, onion powder, cumin, and cayenne and cook for another minute, stirring constantly.
Mash lentils: Use an immersion blender to blend about three quarters of the lentils. (Or use the side of a spatula to mash them instead.)
Combine: In a large bowl, combine the mashed lentils, sautéed vegetables, flax egg, oats, oat flour, and Worcestershire sauce. Use your hands to incorporate the ingredients. Add salt and pepper to taste.
Make the balsamic glaze: Heat the balsamic vinegar, maple syrup, and tomato paste in a small skillet over medium high heat. Cook for about 3 minutes, or until sizzling. Stir well. Remove from the heat.
Pack the meatloaf mixture into 4 (1-cup) oven-safe containers, or into one standard 9x5 inch nonstick loaf pan. Brush with the glaze.
Bake for 25 minutes for the mini meatloaves, and about 35 minutes for one standard loaf, or until heated through.