Mix the ingredients of the dressing in a salad bowl, season with salt. Add in the spinach and mint leaves and let it rest.
In the meantime, cut the chicken breasts in half, horizontally (you will end up with 4 chicken fillets), place on a hot grill pan, and cover each chicken breast with a slice of pineapple, season with black pepper. Grill for around 6-8 minutes, then turn and grill for another 5 minutes (at this stage remove the pineapple and let it grill next to the chicken).
Remove from the heat and let the chicken rest 3 minutes, then, cut it into strips.
Add the chicken to the salad together with sliced pineapple and finely chopped onion, mix before serving.
Vegetarian option: replace the grilled chicken with fried or baked tofu or feta cheese