Step 1Cook the bacon in a large nonstick skillet over medium-high heat until crisp, about 4 minutes. Transfer to paper towels and blot dry. When cool enough to handle, crumble into small pieces. You'll have about 1/3 cup; set aside. Drain the fat from the pan.
Step 2Add the olive oil and garlic to the pan. Cook until the cloves sizzle but do not brown, about 3 minutes. Remove from the heat. Let cool 5 minutes. Use tongs to remove the garlic and discard.
Step 3Stir the lemon juice, vinegar, salt and pepper to taste into the oil. Place the mushrooms in a large bowl. Pour the oil mixture over the mushrooms; use your hands to gently toss slices until well mixed. Toss in the chives. Let rest at least 1/2 hour before serving or refrigerate up to 4 hours.
Step 4To serve, gently toss in the reserved bacon. Taste; adjust seasoning. Serve chilled or at room temperature.