Preheat oven to 190°C/375°F. Transfer tortillas to baking sheet and lightly spray with cooking spray. Lay flat in oven and bake for approx. 10 – 15 min. Meanwhile, grill chicken until cooked through, then chop into small bite-sized pieces. Shred romaine lettuce. Combine salsa, thawed corn, beans, and bouillon in a small bowl.
Top each tostada evenly with chicken, lettuce, and salsa mixture. Enjoy!