In a bowl, mix ground chicken with salt, pepper, parmesan, Dijon, olive oil, lemon zest, and garlic. Form into golf ball–sized portions.
Heat a large skillet over medium-high heat. Place a flour tortilla in the pan, add a tablespoon of the ground chicken mixture in the center, and smash flat using a spatula. The layer of chicken should be quite thin in order for it to cook properly.
Cook 3–4 minutes until golden and cooked through. Flip and cook 1–2 minutes on the other side. Repeat in batches.
To make Caesar dressing, add all ingredients except oil to a blender. Blitz to combine, then stream in oil slowly while blending until emulsified.
Top each taco with Caesar dressing, romaine lettuce, and crushed croutons. Garnish with more parmesan if desired. Serve immediately.