1. Heat the grill to medium heat, while preparing other ingredients.
2. Peel and halve the onion. Slice into half moon shape slices, as thin as possible. On medium heat, add the butter to a sauté pan until fully melted, add the onions and a pinch of salt. Move around to coat. Continue to stir every few minutes as onions begin to caramelize and turn brown, about 15 minutes.
3. While onions are cooking, prepare mushrooms. Wipe them clean with a moist paper towel to remove dirt. Cut off the stem and brush each with half of the oil and balsamic vinegar. Sprinkle with sea salt. Put them on the grill with the gill side up to start and close lid, grill for 3 minutes on each side. Note: the freshness and mushroom may vary the cooking time here. You want them to be fully warmed through, without getting too soggy. Remove and cool to room temperature.
4. Prepare salad. In a large bowl, combine the greens, gorgonzola and the tablespoon of the olive oil and lemon juice. Sprinkle a pinch of salt and pepper, and toss gently. This is only lightly dressed, as the onions and mushrooms will also add some moisture to the salad. Cut the portabellos into slices. Top each salad with a quarter of the mushrooms, cheese and marcona almonds. Add more toppings to taste.