Cut chicken into bite-sized pieces and set aside. Smash garlic cloves with the side of the knife keeping them intact but flattened a bit.
Heat olive oil and smashed garlic in a large skillet over medium-high heat. Sauté garlic for several minutes until golden brown. Remove garlic with a slotted spatula and discard.
Add chicken to hot skillet and cook until golden brown on each side, approximately 3-4 minutes per side. Season with salt and black pepper, to taste. Remove chicken from skillet and set aside.
Add half & half and chicken broth and scrape up any brown bits from the bottom of the pan with a spatula.
Add oregano and grated cheese to skillet and whisk until cheese is completely melted, approximately 3-4 minutes.
Reduce heat to just below medium and add the sun-dried tomatoes and baby spinach. Simmer until tomatoes are softened and the spinach wilts, stirring occasionally about 2-3 minutes
Add chicken and its juices back to skillet and simmer until chicken is heated through, 2-3 minutes. Taste and adjust seasonings, as desired.