Cook spaghetti according to package directions; drain, reserving 1/4 cup of the liquid.
Add olive oil to a medium-sized, nonstick skillet and heat over medium heat.
Crush garlic and add to skillet; cook for one minute.
Halve tomatoes and add to skillet with garlic; cook 1 more minute more, then season with salt and pepper.
Remove skillet from the heat and stir in lemon juice. Coarsely chop watercress.
Add drained pasta, reserved liquid, and watercress to the skillet; stir until everything is well coated.
Top with freshly grated Parmesan, and serve sliced pears on the side.