Preheat oven to 425°F (220°C).
Pulse cauliflower florets (in 2 batches to fit) in food processor until pieces resemble couscous (2 cups/500 mL crumbles). Transfer into large microwaveable bowl. Cover and microwave on HIGH 4 min., or until tender. Cool completely. Transfer to clean tea towel; squeeze out excess moisture.
Place cauliflower back into bowl. Mix in Parmesan and eggs.
Brush melted butter onto 17 X 12-in. (43 x 30-cm) parchment paper-lined baking sheet. Spoon cauliflower mixture into the centre. Use hands to press out mixture into 1/2-in. (1-cm) thick rectangle, about 10 x 8-in. (25 x 20-cm).
Bake 18 to 20 min., or until edges start to turn golden and crust is firm. Remove from oven (preheated oven will also be required in later step) to cool completely. Cut cauliflower “bread” into sixteen rectangles, about 2 x 2 1/2-in. (5 x 6-cm) pieces. Sprinkle Cheddar onto half the rectangles; cap with remaining pieces. Place back into hot oven; bake 8 to 10 min. until cheese melts.
Toss together mixed greens, oil, vinegar, chives and salt. Serve alongside grilled cheese sandwiches.
Add crumbled bacon to sandwiches for bacon grilled cheese bites and serve as a party appetizer.