Preheat oven to 375°F (190°C) and adjust rack to upper-middle position.

If using chicken breasts, slice each breast to ensure even thickness.

Heat chicken stock in a saucepan over medium-high heat until simmering.

Add chicken and 1/2 teaspoon salt to the simmering stock. Reduce heat to low.

Gently simmer until chicken reaches 160°F (71°C), approximately 13-15 minutes.

Transfer chicken to a plate and let cool slightly. Shred into bite-sized pieces.

In a large oven-proof nonstick skillet, heat 3 tablespoons of olive oil over medium heat.

Add onion, broccoli, and 1/2 teaspoon salt to the skillet. Cook, stirring, until vegetables begin to soften (about 6 minutes).

Stir in 1/2 teaspoon black pepper, the remaining tablespoon of olive oil, and halved tomatoes.

Remove the skillet from heat and evenly distribute the shredded chicken over the vegetables.

In a separate bowl, whisk together eggs, 1/2 teaspoon salt, and chopped basil.

Pour the egg mixture into the skillet, ensuring it covers the chicken and vegetables without stirring.

Place dollops of ricotta cheese throughout the frittata.

Bake in the preheated oven until the eggs are just set, about 20 minutes.

Let the frittata rest briefly before cutting and serving. Garnish with whole basil leaves.