Add oil to a pan over medium heat. Add onion and garlic, and sauté until translucent but not browned, about 5 minutes. Add the peas and 3⁄4 cup water. (Note: No water necessary if you’re using frozen peas.) Cover and bring to a boil. Cook about 3 minutes; drain off liquid.
Add tahini, mint, and goat cheese. Using an immersion blender, puree the mixture. Season with salt and pepper. Chill at least 30 minutes. Serve atop baguette rounds, with a garnish of goat cheese and a small mint leaf.