In a medium saucepan, heat thyme sprigs, garlic cloves, bay leaf, tomato, stock and lentils to a boil; simmer over medium heat for 20-25 minutes or until the lentils are tender. Have a small pot of boiling water on hand to add to the lentils if they become too dry during cooking.
Remove and discard the bay leaf and thyme sprigs. Transfer the tomato and garlic to a shallow bowl and mash with a fork; stir the tomato mixture back into the lentils. Stir in oil, lemon zest, vinegar, salt and pepper.
For the Heirloom Tomato Vinaigrette
In medium bowl, whisk together the garlic, vinegar, salt and pepper; slowly drizzle in oil while whisking constantly until emulsified. Stir in the tomatoes and basil.
Heat a large skillet over medium-high heat. Add oil and heat until hot; sprinkle trout with salt and pepper. Add trout, presentation-side down, and thyme sprig to skillet; sear for 3-4 minutes or until evenly browned. Turn trout and sear 1-2 minutes or until browned. Transfer trout to paper towels to absorb excess oil.
Steam the asparagus for 3-4 minutes or just until tender-crisp; toss with oil, salt and pepper.
Place lentils in center of large plate; lay trout and asparagus over the top. Spoon heirloom tomato vinaigrette over trout and asparagus and garnish as desired.