Place the oil in large skillet set over medium-high. When hot, add the mushrooms, garlic and tarragon and cook until tender, about 4 to 5 minutes. Remove from the heat and stir in the juice, vinegar, salt and pepper.
Divide and mound the spinach in the centre of 4 plates. Divide and top spinach with the mushrooms, cheese and almonds. Serve immediately.
Note: Before slicing the oyster mushroom, trim away any tough parts of the lower stem. Before slicing the shiitake mushroom, remove and discard the very tough stem. To toast almonds, place in a single layer in a small baking pan. Bake in a 300 degrees F oven 10 minutes, or until lightly toasted.