- Remove stems from mushrooms; finely chop stems. Set aside caps and chopped stems. Heat skillet over medium heat. Cook bacon until crisp and golden, 4 to 6 min. (reserve bacon fat in skillet). Drain bacon slices on paper towel. Finely chop; set aside.
- Heat skillet containing bacon fat over medium heat. Stir in onion, chopped mushroom stems and thyme; cook until onion has softened, about 5 min. Stir in wine and Worcestershire sauce; cook until most of liquid has evaporated. Mix in mustard. Cool completely.
- Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
- Mix together onion mixture, reserved bacon, breadcrumbs and cheese. Spoon 1 tbsp (15 mL) filling into each mushroom cap. Place caps on lined baking sheet, spacing about 2-in. (5 cm) apart. Bake 10 to 12 min. until mushrooms are tender and filling is golden brown. Serve hot.
• Garnish with chopped fresh thyme, chives or parsley.
• Chop any leftover stuffed mushrooms; toss with pasta for quick dish.