Coarsely chop the mushroom into a fine dice. Or pulse in a food processor, but becareful not to turn it to mush.
In a large saute pan,add olive oil to medium-high heat. Add mushrooms and diced red pepper, saute until mushroom is soft and meaty. This will take about 20 minutes. Add pinto beans, taco seasoning mix, green onions and water. Stir well and contiune to cook until all liquid is evaporated. Distribute mushroom mixture between flour tortillas and top with your favorite taco toppings.