Arrange a 3-oz chicken breast per serving on a cutting board. If necessary, pound the chicken flat to about ½-inch thick. Pat the chicken breasts dry with a paper towel. Then season the breasts with salt, pepper, onion powder, and Italian seasoning. Spread your flour out on a plate, and lightly dredge the chicken in flour. Make sure to shake off any excess flour before continuing.
Drizzle the first amount of olive oil in a pan and heat over medium-high heat on your stove. Once the oil is hot, transfer the dredged chicken to the pan. Cook the chicken on both sides for about 4 minutes per side, until the outside of the chicken has turned golden brown. When you flip the chicken over to cook the second side, squeeze the lemon juice in the pan to infuse the chicken. Transfer the chicken aside to cool on a serving dish for later.
To make the spinach florentine, chop the spinach and toss it in a large pan or shallow pot with the second amount of olive oil. Cook the spinach over low heat until it fully cooks down. Set this aside for a little later. In another pan or small pot (you can use the pan you cooked your chicken in), melt the butter over low heat and add in garlic and the white wine vinegar. Once the garlic becomes fragrant in the butter, pour in the chicken broth.
Turn the heat up on the chicken broth to a simmer. Pour the cream in, stir to combine, and cover the saucepan with a lid. Let the florentine sauce bubble down for a few minutes until it’s a little thicker. Then, add the cooked spinach to the sauce. Stir the sauce together and let it simmer openly until it reduces and thickens around the spinach. Pour the finished florentine sauce over the chicken breasts and serve.