In a heavy 12-inch skillet, heat the olive oil over medium heat.
Add the garlic clove, and cook for 2 minutes stirring constantly.
Remove the garlic, and discard it.
Add all the nuts to the garlic-infused oil, and cook for 5–6 minutes, or until they are browned (stir constantly to prevent burning).
Add the bacon, sea salt (if desired), and black pepper. Cook for 2–3 minutes.
Rinse and dry the watercress. Add it to the oil.
Working quickly, toss the watercress into the mixture, making sure it is well coated and barely heated through (if left too long it loses some of its crispiness).
Season to taste, and serve immediately.