In a dutch oven, heat olive oil over medium heat. Cook onions and celery until softened.
Add sausage and sauté until heated through. Stir in garlic and sauté for about 30 seconds to 1 minute – do not brown.
Add chicken stock and black-eyed peas to the pot. Bring to a boil; cover and reduce heat to simmer. Allow to cook on low until peas are cooked, about 2 to 3 hours.
Stir in collard greens and continue cooking until greens are wilted, approximately 5-10 minutes.
Add vinegar, red pepper flakes, thyme and salt and pepper to taste.