If not using pre-cooked lentils, simmer 1 cup dry brown lentils in 3 cups water for 20-25 minutes until tender but not mushy. Drain well and cool slightly. You need 1.5 cups cooked.

Heat olive oil in a large skillet over medium heat. Add onion and cook for 5 minutes until softened. Add mushrooms and cook for 8-10 minutes, stirring occasionally, until all moisture evaporates and they turn golden. Add garlic and cook 1 minute more. Remove from heat and cool for 5 minutes.

In a food processor, pulse the toasted walnuts until finely ground. Add 1 cup of the cooked lentils, the mushroom mixture, oats, soy sauce, tomato paste, thyme, and smoked paprika. Pulse until combined but still slightly chunky, about 8-10 pulses.

Transfer the mixture to a large bowl. Fold in the remaining 0.5 cup lentils, beaten eggs, salt, and pepper. Mix until everything holds together when squeezed. Press firmly into a greased 9x5 inch loaf pan, mounding slightly in the center.

Bake at 375F for 30 minutes. Meanwhile, whisk together all glaze ingredients in a small bowl.

Remove meatloaf from oven, spread glaze evenly over the top, and return to oven for 20-25 minutes until the glaze is set and a thermometer inserted in the center reads 160F. Let rest 10 minutes before slicing.