Combine squash and thyme in a medium bowl. Crush 1 garlic clove; add to squash mixture. Drizzle with 1 tablespoon oil; sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper. Toss to coat. Arrange squash mixture in a single layer on a baking sheet; bake at 375° for 40 minutes or until squash is tender; stirring occasionally.
Place 1 garlic clove in a mini food processor; process until finely chopped. Add 2 tablespoons oil, celery leaves, parsley, juice, and 1/8 teaspoon salt; process until finely chopped.
Sprinkle 1/4 teaspoon salt and remaining 1/4 teaspoon pepper evenly over trout fillets. Brush fillets with 1 teaspoon oil. Place fillets, skin side down, on a grill rack; grill 5 minutes or until fish flakes easily when tested with a fork. Keep warm.
Slice remaining clove of garlic. Heat a large skillet over high heat; add remaining 2 teaspoons oil. Add sliced garlic, onion, and remaining 1/8 teaspoon salt; cook 2 minutes or until onions begin to brown. Add squash mixture; cook 2 minutes or until hot. Stir in pecans; cook 1 minute. Divide squash mixture evenly among 4 plates; top each with a trout fillet. Spoon 2 tablespoons pesto over each trout fillet.
A couple of issues with the recipe. It calls for a cup of olive oil (crazy for a Cooking Light recipe), but fortunately it doesn't use nearly that much. It calls for 1/2 pecan halfs (whatever that means). I used 1/2 C, but it could easily use less - maybe 1/4 C. That being said, it was excellent. Personally, I would double the vegetable mix (I made it all with half the fish for two of us.) The celery leaf pesto is a great addition - don't skip it. I was going to serve with black quinoa, but it took longer to cook than the package said, so we didn't have it and we didn't miss it. This would be good on it own (with the larger portion of veggies) with just an excellent whole grain artisan bread.