For the chicken: Whisk to combine the orange juice, tequila, lime juice, triple sec, olive oil, chili powder, cumin and garlic in a medium bowl. Place the chicken in a resealable bag or in a bowl and pour the marinade over. Refrigerate for 2 hours and up to overnight.
Preheat a grill or grill pan over medium heat and drizzle with olive oil. Remove the chicken from the marinade and discard the liquid. Sprinkle the chicken with salt and pepper, then grill until cooked through, about 6 minutes per side. Remove from heat, cover with foil and let rest while you prepare the dressing.
For the dressing: Whisk to combine the olive oil, lime juice, orange juice, sugar, chili powder, cumin and some salt in a small bowl.
For the salad and sandwich: Dice the grilled chicken and place in a large bowl with the cherry tomatoes, cilantro, celery, avocado, mango and some salt and pepper. Drizzle over the dressing and toss to coat.
Place a lettuce leaf on the bottom half of each croissant and top with chicken salad. Place the tops on each sandwich, then cut in half and place a toothpick in each half to serve.