Season the chicken thighs with salt, pepper, and Italian seasoning.
Heat the olive oil in a large deep skillet over medium-high heat. Sear the chicken for 4 to 5 minutes per side until browned, then transfer it to a plate.
Add the onion to the skillet and cook for 5 to 6 minutes until softened. Stir in the garlic and tomato paste, and cook for 1 minute.
Add the crushed tomatoes, dairy free milk, red pepper, and salt. Stir well and simmer for 8 minutes.
Return the chicken and its juices to the skillet. Simmer uncovered for 12 to 15 minutes until the chicken is cooked through and the sauce has thickened.
Stir in the spinach and cook for 2 minutes until wilted.
Taste and adjust the seasoning, then garnish with basil and serve over rice or pasta.