In a food processor, combine 1 cup of the lentils, the potatoes, garlic, tomato paste, tamari, onion flakes, flax meal, balsamic, tahini, oregano, thyme, celery seed, and black pepper. Puree briefly, until fairly well combined but not completely smoothed out. Add the remaining 1 cup lentils, the oats, and the pumpkin seeds and pulse a couple of times, scraping down the bowl as needed, until the mixture is fairly well combined but still has texture—take care not to overprocess. Remove the blade and use a silicone spatula to mix a little more by hand.