Build the Flavor Base: In a large, heavy-bottomed pot or Dutch oven, heat 2–3 tablespoons of water over medium-high heat. Add the diced onion and sauté for about 5 minutes, stirring occasionally, until soft and slightly translucent. If the onion starts to stick, splash in a little extra water to loosen it
Add the Core Vegetables and Seasonings: Toss in the celery, potato cubes, carrot slices, and mushrooms (if using). Sprinkle the dried sage and rosemary over the vegetables, stirring well to coat them in the herbs and allow the flavors to bloom.
Simmer with Lentils and Broth: Crumble the vegetable bouillon cube into the pot, then pour in 4 cups of water. Add the rinsed lentils, stirring to combine everything evenly. Bring the mixture to a rolling boil, then immediately lower the heat to a gentle simmer. Cover and cook for 10 minutes, stirring every few minutes to prevent the lentils from sticking to the bottom of the pot. The potatoes should just begin to soften.
Cook the Broccoli and Thicken the Stew: Add the broccoli florets to the pot. Continue cooking for another 8–10 minutes, uncovered this time, until the lentils have broken down into a creamy consistency and the broccoli is tender yet bright green. Stir occasionally to keep everything well-mixed.
Final Seasoning and Greens: Stir in Bragg’s liquid aminos or soy sauce, adjusting salt and black pepper to taste. If using leafy greens, add them in now, cooking just long enough for them to wilt (about 1–2 minutes).
Serve and Enjoy: Ladle the thick, hearty stew into bowls, garnish with chopped fresh parsley if desired, and serve hot. Pair with crusty bread or a side of rice for an extra-filling meal.