If the baby octopus isn’t pre-cleaned, remove the beak and ink sac, then pat dry.
Heat olive oil in a heavy-bottomed pot over medium-high heat and sear octopus 2–3 minutes per side until reddish-brown; remove and set aside.
Reduce heat to medium, add garlic and red pepper flakes, and sauté 1 minute until fragrant.
Pour in white wine and scrape up browned bits; simmer 1 minute, then stir in diced tomatoes, oregano, salt, and pepper and bring to a gentle simmer.
Return octopus to the pot, cover, reduce heat to low, and simmer 45–60 minutes until tender.
Remove from heat, stir in parsley and lemon juice, adjust seasoning, and serve.