Take a sauce pan. Add one cup of water and guava cubes, then boil it for 5-6 minutes on medium flame, let it cool down.
Once cool down then add the prepared guava mixture, strawberries into a juicer jar and blend it to make puree. Remove the prepared puree, strain it, discard the remaining part and keep aside.
Heat water into an another pan till boiling point. Add black tea, sugar and mix well, boil for 2 minutes. Strain it in a pitcher and let it cool down. Once completely cool, then add lemon juice and keep in fridge till chilled.
Lastly, mix the guava puree in the prepared lemon tea and mix well.
Take serving glasses, add ice cubes and pour guava tea.
Garnish with mint, lemon slice and serve chilled.