In a medium nonstick skillet, heat olive oil over medium-high. Add zucchini, garlic, and thyme; season with salt and pepper. Cook, stirring occasionally, until zucchini is tender and golden brown in spots, about 5 minutes. Transfer to a medium bowl and let cool to room temperature (or refrigerate, up to overnight; bring to room temperature before continuing). Add ricotta, lemon zest, and lemon juice, and stir to combine. Season with salt and pepper.