I take cooking inspiration from all cultures, and nobody does stuffed mushrooms like the Italians! With the combination of cheeses and spices, this is usually a rather indulgent dish, but the veggies and pine nuts in this vegan version add lots of nutrition and protein. Mangia!
Preheat the oven to 350 degrees F and line a baking sheet with parchment paper. Arrange the mushroom caps on the prepared sheet cavity-sides up and brush them with extra oil. Set aside for now.
Heat the oil in a large skillet over medium heat. Add the chopped mushroom stems, fennel, sun-dried tomatoes, and garlic, and sauté until the fennel becomes tender (about 10 minutes).
Transfer the mixture to a medium-sized bowl and mix in the basil, flax egg, and pine nuts, then season it with salt and pepper.
Place the filling in the mushroom cavities and press down to fill well, but make sure not to overfill.
Bake until the mushrooms are tender and the filling is heated through (about 20 minutes).
Let cool briefly before serving. (They can be served warm or at room temperature.)