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