Take the top off the tomatoes then, using the handle end of a teaspoon, scrape out the core and seeds, ensuring you leave a reasonably thick shell and do not pierce the sides. Salt the insides of the tomatoes and leave upside down to drain for 30 minutes.
Heat the olive oil in a pan and gently fry the pancetta or bacon until gold and lightly crisp. Fold the bacon into the ricotta along with the lemon zest, oregano and half the basil leaves, torn. Season.
Blot the insides of the tomatoes with kitchen towel. Spoon in the stuffing, serve with the reserved basil leaves and a drizzle of extra virgin olive oil.