Heat the oil in a deep saucepan or steep-sided stir-fry pan. Add the onions and sauté over medium heat until golden.
Add the kasha and stir in to coat with the oil in the pan. continue to sauté, stirring often, until the kasha is nicely toasted and the onions lightly browned here and there, about 7 minutes.
Pour in the broth or water with bouillon cubes and bring to a slow boil.
Stir in the mushrooms, then lower the heat and simmer uncovered until the liquid is absorbed, about 15 minutes. Stir gently only once during this time, as you don’t want the kasha to get mushy.
Meanwhile, cook the pasta in plenty of rapidly simmering water until al dente, then drain.
Add the cooked pasta to the cooked kasha in the pan if it's roomy enough. Otherwise combine the kasha mixture and pasta in a serving container. Toss together gently with fresh parsley and/or dill as desired, and season with salt and pepper. Serve at once.