Preheat your oven to 350°F (175°C) and grease a loaf pan or line it with parchment paper.
In a large mixing bowl, combine the cooked lentils and quinoa. Use a fork to mash the lentils slightly for better texture.
Heat olive oil in a pan over medium heat and sauté the chopped onion, garlic, carrot, and celery until soft (about 5 minutes). Add this mixture to the lentils and quinoa.
Stir in the breadcrumbs, ground flaxseed mixture, soy sauce, nutritional yeast, thyme, smoked paprika, salt, and black pepper. Mix well until all ingredients are fully incorporated.
Transfer the mixture to the prepared loaf pan and pack it down firmly. Smooth the top with a spatula.
Bake in the preheated oven for 45 minutes, or until firm and slightly crispy on the edges.
While the meatloaf is baking, prepare the gravy. In a saucepan over medium heat, combine the vegetable broth, soy sauce, onion powder, garlic powder, and black pepper. Bring to a simmer.
Gradually add the cornstarch slurry, stirring constantly until the gravy thickens (about 2 minutes). Remove from heat and set aside.
Once the meatloaf is done, let it sit for about 10 minutes before slicing. Serve warm with the rich gravy drizzled over the top.
Notes
Let the meatloaf sit for 10 minutes before slicing for better texture.