Place the chicken breasts on a cutting board and pat dry with paper towels.
Season both sides of the chicken breasts with 1 teaspoon salt, 1/2 teaspoon black pepper, and 1 teaspoon garlic powder.
In a large skillet, heat 2 tablespoons olive oil over medium-high heat until shimmering.
Add the chicken breasts to the skillet and cook for 6-7 minutes on one side without moving them.
Flip the chicken breasts and cook for another 6-7 minutes, or until the internal temperature reaches 165°F (74°C). Remove chicken from skillet and cover with foil to keep warm.
While the chicken cooks, place the quartered baby potatoes in a large pot and cover with cold water.
Add a pinch of salt and bring to a boil over high heat. Reduce heat to medium and simmer until potatoes are tender, about 15 minutes.
Drain the potatoes and return them to the pot. Add 2 tablespoons unsalted butter, 1/4 cup whole milk, 1/2 teaspoon salt, and 1/4 teaspoon black pepper.
Mash the potatoes until smooth and creamy. Cover and set aside to keep warm.
In a separate skillet, heat 1 tablespoon olive oil over medium heat.
Add the minced garlic and sauté for 30 seconds until fragrant.
Add the sliced zucchini and red bell pepper to the skillet and cook for 5 minutes, stirring occasionally.
Add the baby spinach, 1/4 teaspoon salt, and 1/4 teaspoon black pepper, and cook for an additional 2 minutes until spinach is wilted.
Serve each chicken breast with a scoop of garlic mashed potatoes and sautéed vegetables on the side.