Adjust oven rack to middle position and preheat to 425°F.

Place 3 pieces of paper towel on a microwavable plate.

Lay bacon on paper towel.

Microwave on high power until bacon has just begun to cook and some of the fat has rendered out, about 1 to 1 1/2 minutes.

Coil each piece of bacon around each cup in a muffin tin, making sure the bottom of the cup is covered.

Place any of the additional fillings (spinach, peppers, or leeks) in the bottom of the cup.

Crack an egg into each cup on top of the fillings.

Bake until the whites of the eggs are set but the yolk is still runny, about 10 minutes.

Serve immediately.

For Spinach Filling: Melt the butter in a medium skillet over medium heat.

Add the garlic and cook until fragrant, about 30 seconds.

Add spinach and cook until it has wilted and all the water has evaporated, about 2 minutes.

Season to taste with salt and pepper.

For Pepper Filling: Heat olive oil in a medium skillet over medium heat until shimmering.

Add onion and cook until it just begins to soften, about 4 minutes.

Add peppers and cook until peppers are just cooked through, about 5 minutes.

Season to taste with salt and pepper.

For Leek Filling: Melt the butter in a skillet over medium high heat.

Add the leek and cook until soft, about 8 minutes.

Add cream and reduce heat to low.

Cook until cream has just begun to thicken, about 10 minutes.

Season to taste with salt and pepper.

For Brussel Sprout Filling: Heat the olive oil in a skillet over high heat until it just begins to smoke.

Add the brussel sprout leaves and cook, stirring constantly until the leaves are just beginning to char, about 1 minute.

Remove from pan and toss with lemon zest.

Season to taste with salt and pepper.