Heat a large skillet over med-high heat. Add bacon, cooking for about 10 minutes or until desired crispiness. Drain on a paper towel lined plate and set aside.
Meanwhile, whisk eggs in a large bowl with salt & pepper to taste and mix mayo, garlic and hot sauce together to make aioli. Without wiping pan clean, add onions and fry, seasoning with a bit of salt & pepper, for 5 minutes until tender. Remove and set aside.
Add a bit of butter if the pan needs greasing, then add eggs, scrambling until just set, about 2 minutes. Remove from heat.
Cut open croissants, then add a slather of hot sauce aioli. Add a slice of bacon. Top with a bit of scrambled eggs, some red onions and then arugula. Serve and enjoy!
TO MAKE AHEAD: Assemble croissants up to a day in advance with everything stuffed inside except for arugula and aioli. When ready to serve, add all croissant sandwiches to a parchment-lined baking sheet and reheat in a 350 F oven for 10 minutes. Open each back up and add arugula and aioli, then serve and enjoy!