Cut red and banana peppers into strips, discarding seeds. Pack peppers into 5 hot 1-pint jars to within 1/2 in. of the top. Divide the onion, garlic and oil among jars., In a large saucepan, bring water, vinegar, sugar and salt to a boil. Carefully ladle hot liquid over pepper mixture, leaving 1/2-in. headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot liquid. Wipe rims. Center lids on jars; screw on bands until fingertip tight., Place jars into canner with simmering water, ensuring that they are completely covered with water. Bring to a boil; process for 15 minutes. Remove jars and cool.