Preheat oven to 400°F. Add the peppers, onions and mushrooms in a large bowl along with the oil and fajita seasoning. Toss well to combine, trying to coat the vegetables with all of the spices. Place vegetables in a single layer on a baking sheet (may need two depending on size) and place in the oven.
Roast for 25 to 30 minutes, or until tender, stirring at least once making sure the vegetables don't burn.
While the vegetables are cooking, make the sauce. Place the cashews, oat milk, green chiles and salt into a blender and puree until very creamy and smooth. Depending on the power of your blender, this may take up to 5 minutes. Taste, adding more salt if needed. The consistency of the sauce should be a thickened cheese sauce; if too thick, add more oat milk. Divide vegetables among warmed tortillas and top with queso sauce!
This nutritional information refers to each serving of the entire recipe and not just the products used as ingredients.