Garlic (for both the marinara and broccoli) / Shallots - Prep as directed and combine garlic and shallots for the marinara. Store garlic for the broccoli in a separate container. (Can be done up to 5 days ahead)
Broccoli - Chop broccoli into florets. (Can be done up to 5 days ahead)
Chicken - Halve chicken breasts. Sprinkle Italian seasoning and some salt and pepper on both sides and tenderize with a fork. (Can be done 1 day ahead)
Heat a small saucepan over medium-high heat. Add cooking oil and then garlic (the portions for the marinara) and shallots to heated oil. Saute for ~2 minutes and then add crushed tomatoes with salt and black pepper. Reduce heat and simmer for ~4 minutes to let the flavors come together.
While sauce simmers, heat a large saute pan with cooking oil (the portion for the chicken) over medium-high heat. Add chicken and sear on both sides until golden brown and cooked through, 5 to 6 minutes. Set chicken aside and cover to keep warm. Return pan to heat.
To heated pan, add broccoli, garlic (portion for the broccoli) and water. Cover tightly with a lid or foil. Steam broccoli until tender, 5 to 6 minutes. (Alternatively, steam broccoli and garlic in microwave-safe pan covered with a damp paper towel, 2 ½ to 3 minutes on high.)
Season broccoli with lemon juice and some salt and pepper. Toss with cashews.
Spoon marinara over chicken and top with basil. Enjoy with broccoli on the side!