For the meatballs, into a medium-sized pot, add dried lentils and 1½ cups water. Bring to a boil, then cover and reduce to low heat. Simmer for approximately 25 minutes or until lentils are softened and cooked through.
Into a small bowl, add flaxseed and 3 tablespoons water. Set aside to thicken while the lentils are cooking.
Into a food processor, add cooked green lentils, flaxseed mixture, cremini mushrooms, shallot, garlic, bread crumbs, salt, black pepper, and dried oregano. Blend on high speed until all ingredients are well combined. Roll mixture into 2-inch balls. You will have approximately 20 lentil meatballs.
Into a large skillet, heat olive oil over medium-high heat. Add lentil meatballs, and cook, turning frequently, until browned evenly all around.
For the sauce, into a large skillet over medium-high heat, add 2 tablespoons vegan butter. When butter is melted, add mushrooms and cook 2 minutes. Add garlic and continue cooking for 1 minute. Remove to a paper towel-lined plate.
To the same skillet over medium-high heat, add remaining 2 tablespoons vegan butter. Once butter is melted, quickly whisk in all-purpose flour. Whisk in vegan beef broth and dry white wine. Bring to a boil for 1 minute, and remove from heat.
Stir in Dijon, sour cream, salt, black pepper, and ground nutmeg. Add mushroom mixture back into the pan and gently stir to combine with sauce.
Prepare pasta according to package directions. Before draining, reserve ½ cup of the still-hot water. Gradually stir in reserved pasta water ¼ cup at a time to thin sauce to desired consistency.
To serve: Toss sauce with prepared pasta and top with lentil meatballs. Garnish with Italian flat leaf parsley and serve warm.