In a sauté pan over medium heat, add oil and peppers and sauté 4 minutes.
Add bell pepper and thyme and sauté until tender, about 5 minutes more. Set aside to cool.
Preheat oven to 375 F (190 C) and grease an 8-inch (20 cm) square pan. Whisk buttermilk, vegetable oil, eggs, sugar and lemon juice to combine.
In a separate bowl, stir together cornmeal, flour, green onion, coriander, lemon zest, baking soda, salt, cumin and cayenne pepper. Add to buttermilk mixture and whisk until smooth (batter will be very liquid).
Stir in cooled pepper mixture and pour batter into prepared pan. Bake for 15 to 18 minutes, until top is a light golden brown and cornbread springs back when touched.
Confetti cornbread is best served warm, but this will keep well for a day in an airtight container.