Heat olive oil in a large saucepan over medium heat until shimmering. Add the sliced onions and cook, stirring occasionally, until they become soft and translucent, about 5-7 minutes, filling your kitchen with a fragrant aroma.
Add the minced garlic and cook for another minute until fragrant, stirring constantly to avoid burning.
Place the cleaned octopus pieces into the pot and cook for 3-4 minutes, allowing them to release moisture and start to brown slightly.
Pour in the red wine and bring to a simmer, scraping the bottom of the pan to deglaze and incorporate any flavorful browned bits.
Add the crushed tomatoes, bay leaf, and a cinnamon stick to the saucepan, stirring well to combine all ingredients into a rich sauce.
Reduce the heat to low, cover the pot, and let it simmer gently for about 1.5 to 2 hours, until the octopus is tender and the sauce has thickened to a glossy, deep-red glaze.
Remove the cinnamon stick and bay leaf, then taste the stew and season with salt and pepper as needed, adjusting the seasoning for perfect flavor.
Serve the stew hot, spooned over crusty bread or accompanied by your favorite side, showcasing the tender octopus in a rich, aromatic sauce.