Currently one of the main promoters of the guitar in Portugal, his activity includes the organisation of music events, along with teaching, performing, composing and producing.

Graduated as teacher of classical guitar from Conservatorio Nacional de Música de Buenos Aires, he also studied with Eduardo Isaac, Omar Cyrulnik, Miguel Ángel Girollet, Maria Isabel Siewers and several others. He also attended master classes with David Russell, Segiswald Küijken, Leo Brouwer and Rosalyn Tureck, among others.

As a soloist, he has performed in various halls in Argentina and Europe, such as Teatro General San Martín of Buenos Aires, London's Bolivar Hall and St. James Church of Picadilly (where he played his own compositions) and Palácio dos Capitães-Generais (Azores). He also plays regularly with chamber ensembles in different configurations, playing in venues such as Coliseu do Porto, Casa da Música Porto, and in Coimbra - Capital da Cultura.

As a teacher, Oscar Flecha has given numerous courses and master classes in Santo Tirso, Lousada, Porto, Madeira, etc.. He has been a judge in several national and international guitar competitions.

He was founder and artistic director of the festivals "Encontros de Guitarra do Porto" in 1994 (Oporto's first guitar festival) and of the "Santo Tirso International Guitar Festival" also in 1994. He was a founding member and president of Legato – Associação de Arte e Guitarra de Portugal and editor of Colecção Legato "Música Portuguesa para Guitarra". From 2008 to 2013, he was responsible for the programme "Seis Cordas – Seis Momentos", held in Santo Tirso.

He is the founder of Portotango Ensemble, which focuses on the performance of the music of Buenos Aires.

Since 2015, Oscar has led the Borderline ensemble, a fusion music project combining acoustic and electric, classical and popular styles. His latest album, "Santo Tirso Impressions", is made up of original compositions inspired in the artwork contained in Santo Tirso's International Museum of Contemporary Sculpture, and used as the soundtrack of Joaquim Pavão's film, Sculp.

In 2019, he was awarded the Gold Medal for Cultural Merit by the Council of Santo Tirso.

He currently teaches at Centro de Cultura Musical Music Conservatory in Santo Tirso / Famalicão.