Season and cook the chicken: Season the chicken breasts with salt, pepper, and crushed garlic. Heat 1 teaspoon of olive oil in a large skillet or pot over medium heat. Add the chicken and cook for about 10 minutes, turning occasionally, until golden brown on all sides.
Add the leek and zucchini: To the same pot, add the sliced leek and zucchini. Cook uncovered for about 5 minutes, stirring occasionally, until the vegetables begin to soften.
Incorporate the peas, asparagus, and broth: Add the peas, asparagus, and ½ cup of chicken broth to the pot. Sprinkle in the dried oregano. Cover and cook for another 10 minutes, or until the chicken is fully cooked (internal temperature of 165°F or 75°C) and the broth has almost completely evaporated.
Finish with spinach, tomatoes, and yogurt: Add the fresh spinach and halved cherry tomatoes to the pot. Stir in ½ cup of plain yogurt, mixing gently to combine it with the remaining broth and create a light, creamy sauce. Cook for an additional 2-3 minutes, just until the spinach wilts and the tomatoes soften slightly.
Serve immediately: Remove from heat and serve the Spring Chicken hot, ensuring each plate has a chicken breast and a generous portion of the colorful vegetables and sauce.