Creating your own Slow Cooker Chicken Marsala is simple when you follow these clear steps:

1. Sauté Vegetables: In a skillet, heat olive oil over medium heat. Add the onions and mushrooms. Sauté until softened, about 5 minutes, then transfer to the slow cooker.
2. Prepare Chicken: Season each chicken breast with salt, pepper, thyme, and oregano.
3. Arrange in Slow Cooker: Place the seasoned chicken breasts on top of the sautéed onion and mushroom mixture in the slow cooker.
4. Add Liquids: Pour the Marsala wine and chicken broth over the chicken. Ensure that the liquid covers the chicken sufficiently.
5. Set Slow Cooker: Cover and cook on low for 4-6 hours or on high for 2-3 hours, until the chicken is tender and cooked through.
6. Thicken Sauce (Optional): For a thicker sauce, mix the cornstarch with water, then stir into the slow cooker during the last 30 minutes of cooking.
7. Garnish: When done, remove the chicken and spoon the sauce over it. Garnish with fresh parsley before serving.

Following these straightforward steps will ensure you create an incredible dish, bursting with flavor and ensuring satisfaction at your dinner table.