Drizzle olive oil in the bottom of your slow cooker.
Add the chopped onion, garlic, carrots, and celery. You can sauté them first if you want extra flavor, but it’s not required.
Place the chicken breasts or thighs on top of the vegetables.
Pour in the chicken broth until everything is just covered.
Add oregano, salt, and black pepper. Give it a light stir to combine.
Cover and cook on Low for 6 to 7 hours, or on High for about 3 to 4 hours, until the chicken is tender.
Once the chicken is cooked, remove it with a fork and shred it gently, then return it to the pot.
Stir in the lemon juice and lemon zest right before serving. This keeps the flavor fresh and bright.
If you’re adding spinach or zucchini, toss them in during the last 20 minutes of cooking so they stay green and tender.
Taste and adjust seasoning if needed. Serve warm, drizzled with a bit of olive oil or topped with fresh herbs if you like.