Lightning UI Date Time Format

<lightning:formattedDateTime aura:id="thresholdRunOn"
                             value="your date time value"
                             month="short"
                             day="numeric"
                             year="numeric"
                             hour="2-digit"
                             minute="2-digit"
                             second="2-digit"
                             hour12="true"
                             timeZone="{!$Locale.timezone}"/>

Output:
The above example will return a value like this ==> Feb 20, 2018, 9:43:00 PM

Note: Properties value can be change based on your requirement.