Toss tomatoes, garlic, oregano with 2 t. oil. Season with salt and pepper, roast at 425°F until the tomatoes are blistered.
Scrape tomato mixture into the bowl of a food processor reserving half the tomatoes for plating. Blend with cauliflower, with processor running, slowly add 2 T. olive oil then add enough pasta water to make a smooth sauce. Adjust seasoning to taste.
Toss spaghetti with sauce. Plate with blistered tomatoes and wild arugula.