Add at least 4 quarts of water to a pot for pasta. Bring to a boil. Add pasta when boiling. (Do other steps while waiting)
In a small saucepan, add the two chicken breasts. The pan should be large enough that the two breasts can lay on the bottom side by side, but not much bigger than that. Add lemon, peppercorns, salt and oregano. Add enough water to cover chicken and then bring to a boil. Once boiling, boil for another 10 minutes or until chicken is no longer pink in middle (165 degrees F.) Once cooked, drain water and let chicken cool. Chop chicken into bite sized pieces. (Do other steps while waiting)
While pasta and chicken are cooking, make pesto. Chop garlic on high in food processor until chunks are small. Add basil, parmesan, olive oil and pine nuts. Process on high for about a minute, scraping down sides if needed.
Cut cherry tomatoes in half. Drain pasta. Add pasta to a bowl. Top with pesto, chicken and cherry tomatoes. Toss well. Salt and pepper to taste and serve.