For the guacamole, in a smaller bowl mash the avocado, toss in the lime juice, diced red onion, and tomato. Mix it nicely and season with salt and pepper.
Warm your whole-grain tortilla in a pan, for less than a minute. Start filling it with all of your ingredients. In tortillas, I like my mushrooms fresh, however, if you absolutely hate the idea of fresh mushrooms, cook them first.
To finish it all off, squeeze some lime on top and sprinkle salt and pepper. Wrap it up and dig in!