Line a plate with a paper towel. Cut bacon into 1/2" dice. Place bacon in a medium non-stick pan over medium heat (no need to preheat) and cook, stirring occasionally, until crisp, 5-8 minutes. Remove bacon to towel-lined plate. Carefully dispose of rendered fat. While bacon cooks, prepare ingredients.

On a separate cutting board, peel and mince shallot. Coat a muffin tin with cooking spray. Place each puff pastry square in muffin tin and slightly lift and press dough into cups. Dough should cover bottoms and sides, with corners of each dough square sticking over edges. Freeze muffin tin. While pastry chills, make quiche filling.

Combine liquid egg, milk, 1 Tbsp. shallot (reserve remaining for salad), 1/4 tsp. salt, and 1/4 tsp. pepper in a medium mixing bowl.

Remove muffin tin from freezer and place on prepared baking sheet, in case of drips. Divide bacon and cheese between cups, then fill cups 2/3 full with quiche filling. Roll and crimp quiche edges. Bake until dough browns and filling is set (doesn't jiggle when pan is tapped), 15-22 minutes. Rest quiches 5 minutes before carefully removing from muffin tin. While quiches cook, make salad.

Clean mixing bowl used for egg mixture. Peel and core apple. Cut into 1/2" dice. Combine apple, arugula, shallot (to taste), Italian dressing, 1/4 tsp. salt, and 1/4 tsp. pepper in cleaned mixing bowl. Toss to coat.

Place two mini-quiches on a plate and serve salad on side.