Place asparagus in a steamer over 1 inch of boiling water, and cover. Cook until tender but still firm, about 2 to 6 minutes. Drain, cool in a bowl of ice water, drain on paper towels, and place on a serving platter.
In a medium saucepan, heat 1 tablespoon olive oil or medium-low heat. Add the garlic and cook and stir until fragrant, 2 to 3 minutes. Add the pancetta, and continue to cook and stir for 8 to 10 minutes, or until browned.
Remove the pan from the heat and stir in the remaining 3 tablespoons olive oil, lemon juice and Dijon into the garlic-pancetta mixture. Pour the sauce over the asparagus.