If you have Google Chrome (or Brave Browser), you can connect your Coinbase Wallet to Matcha via the Coinbase Wallet Extension. Once you have the Browser Extension installed, you can connect to Matcha. Here's how:
Click on the Connect Wallet button from either the drop-down in the top-right hand corner, or in the Trade Module.
Click on "Connect Coinbase Wallet".
When the pop-up appears on your browser, click "Connect".
You can now trade on Matcha with your Coinbase Wallet!
In order to connect Matcha to Coinbase on a Mobile Device, it is best to use Coinbase's built in browser in Coinbase Wallet.
Open the Coinbase Wallet app on your mobile device.
Click on the Browser button in the bottom-middle of the screen (should be a globe) to open the browser.
Navigate to matcha.xyz in the URL field at the top of the page.
At the bottom of the page, select the Connect Wallet button.
Click Connect Wallet.
Click Coinbase Wallet from the list of options.
Start trading on Matcha!