Preheat oven to 425F.
Cook the cannelloni according to package instructions. Drain and pat dry with paper towels.
Heat olive oil and butter in a pot over medium heat then stir in the garlic, and cook for about a minute, constantly stirring.
Add quartered cherry tomatoes to the pot and cook over medium-low heat for 4 minutes.
Add in the ricotta cheese and the feta cheese. Cook for 2 minutes.
Add spinach and sauté, stirring, until just wilted, about 2 more minutes.
Season with salt and pepper, and remove from heat.
Stuff the mixture into the cannelloni tubes with a small spoon or a piping bag.
Arrange the cannelloni shells down inside of a baking dish or a clay baker.
Top with the tomato sauce and sprinkle with the shredded mozzarella cheese.
Bake in oven for 20 minutes or until sauce is bubbly and cheese is golden on top.
Allow it to cool for about 10 minutes before serving.