1. Defrost dough and cut into 15 squares (three rows of five). Spray 15 muffin cups with cooking spray and gently press the dough into the cups and up the sides. Trim excess dough so there’s no dough hanging over the edges. Set aside.
2. Heat oil in a large frying pan over medium heat. Add the onion and season with 1/2 teaspoon salt. Sauté until starting to brown, about 10 minutes.
3. While the onion is cooking, dice the chicken and pastrami. Add to the pan along with another 1/2 teaspoon salt and parcook for five minutes. Combine sweet sauce and mustard and pour over chicken and onions. Cook another two minutes and transfer to a bowl. Allow to cool.
4. Meanwhile, prepare the spinach layer: Rinse the frying pan and spray with cooking spray. Add garlic and sauté until fragrant, about 30 seconds. Add the spinach with the remaining one teaspoon salt and allow it to wilt completely. Remove to a bowl, leaving any liquid behind in the pan.
5. Allow the spinach to cool, then add the eggs and panko crumbs. Mix to combine.
6. Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius). Spoon the chicken mixture into the dough in each muffin tin, filling them until mostly full. Cover with a spoonful of spinach mixture. The chicken should be completely covered and not showing underneath. Bake for one hour. Serve warm or hot.