In large frying pan over medium-high heat, place 1 tablespoon olive oil; when hot add pecan halves. Stir to coat; let toast 1 to 2 minutes, stirring constantly, or until nuts are deep rich brown. Remove from heat, place pecans on paper towels to drain. Set aside.
Place pan over medium heat and place remaining 2 tablespoons olive oil in pan. When hot, add onion and garlic and saute 3 to 4 minutes, stirring constantly, until onion slices are softened. Add squash, zucchini and pepper slices; stir constantly, saute vegetables until tender, approximately 5 to 7 minutes.
Remove from pan and season with lemon juice, oregano, salt and pepper to taste. Stir in reserved toasted pecans and serve with grilled pork, fish or chicken.