Drain the canned pineapple in a sieve and reserve the juice for the marinade.
Pat the chicken breasts dry and cut into bite-sized pieces. Thread the pieces onto wooden skewers, spacing them evenly. Place the skewers in a baking dish.
In a bowl, combine the reserved pineapple juice, finely chopped onion, chopped garlic, cinnamon, paprika powder, and sambal oelek. Season with salt and pepper to taste.
Pour the marinade over the chicken skewers in the baking dish, ensuring they are well coated. Refrigerate and marinate for 10 minutes, then turn the skewers over and marinate for another 10 minutes.
While the chicken marinates, clean the rocket and divide among serving plates to create a bed. Top with the drained pineapple pieces. Add cherry tomatoes if using.
Remove the chicken skewers from the marinade and set aside on a plate. Reserve the marinade.
Heat roughly 1 tablespoon of oil in a pan over medium-high heat. Add the reserved marinade and simmer for 2–3 minutes, stirring occasionally, until it thickens slightly.
In the same pan, cook the chicken skewers for 4–5 minutes per side over medium-high heat, until golden brown and the chicken reaches an internal temperature of 74°C (165°F).
Arrange the chicken skewers on the rocket and pineapple bed, drizzle with the thickened marinade, and serve.