Season the chicken breast evenly on both sides with sea salt, black pepper, and dried oregano.
Heat the olive oil in a large skillet over medium-high heat until shimmering.
Place the chicken in the skillet and sear for 5-7 minutes per side until golden brown and cooked through to an internal temperature of 165°F.
Remove the chicken from the skillet and set aside on a plate to rest.
In the same skillet, add the diced yellow onion and minced garlic, sautéing for 2-3 minutes until translucent and fragrant.
Pour in the chicken broth, coconut milk, sun-dried tomatoes, and nutritional yeast, whisking to combine and scraping up any browned bits from the bottom of the pan.
Simmer the sauce for 4-5 minutes over medium heat until it begins to thicken into a creamy consistency.
Add the fresh spinach to the skillet and stir for 1 minute until just wilted.
Return the chicken to the pan, spooning the warm sauce over the top to coat before serving.